Materials Guide · Liquid Silicone Rubber
What Is Liquid Silicone Rubber? Properties, Uses & Benefits
Liquid silicone rubber (LSR) is one of the most widely specified elastomers in demanding molded parts. In this guide, our engineering team explains what LSR is, what it is made of, how it is molded, where it performs well, and where it needs careful planning.
LSR is a two-part, platinum-cured silicone elastomer that arrives as a liquid and is typically shaped by injection molding into finished, flexible parts.
What Is Liquid Silicone Rubber (LSR)?
Liquid silicone rubber is a synthetic elastomer based on a silicone polymer. In its uncured state it is a flowable material supplied as two components, usually labeled A and B. The two parts are metered and mixed immediately before molding, then cured inside a heated mold to form a solid, rubber-like part. Because the material flows, it can fill thin sections and fine features that are difficult to achieve with other rubbers.
Most LSR used in production is platinum-cured, meaning a platinum catalyst drives the crosslinking reaction. This cure system produces a stable network without the by-products associated with some other curing chemistries, and it is the reason platinum-cured silicone is often selected for medical and food-contact work.
How LSR compares with related materials
Silicone is a family of materials, and several products share the name. The table below clarifies how LSR differs from the other forms engineers often confuse with it.
| Material | Form and role |
|---|---|
| Liquid silicone rubber (LSR) | Two-component liquid elastomer, mixed and injection molded, then cured into finished elastic parts. |
| Silicone oil | A fluid that does not cure into an elastomer, so it cannot form a rubber part on its own. |
| Silicone sealant | A product intended for applying and curing a joint or bead, not for molding precision components. |
| Solid silicone rubber (HCR) | A high-consistency, dough-like compound processed on mills and typically formed by compression molding or extrusion. |
Why it matters
When a drawing or purchase order says "silicone," confirm which form is meant. An LSR part, a compression-molded HCR part, and a sealant bead have different tooling, process and cost profiles.
Is Liquid Silicone the Same as Rubber?
Functionally, yes: once cured, liquid silicone rubber behaves like rubber. It stretches, recovers its shape, seals against mating surfaces and absorbs compressive loads. Chemically, however, it is not natural rubber. Natural rubber is a polyisoprene derived from latex, while LSR is built on a polysiloxane backbone with a silicon-oxygen structure. That chemistry is the source of its heat resistance, its flexibility at low temperatures and its generally stable behavior in weather and ozone.
The more practical comparison for a design team is between LSR and high-consistency rubber (HCR), which is also a silicone. The differences lie mainly in the starting form, the processing method and the typical production route.
Liquid silicone rubber
Starts as a pumpable liquid
Metered, mixed and injected through automated equipment. Well suited to high-volume, repeatable parts with fine detail.
High-consistency rubber
Starts as a stiff compound
Milled and shaped by compression molding or extrusion. Often used for larger, simpler profiles and sheet forms.
What Is Liquid Silicone Rubber Made Of?
An LSR compound is a formulated system rather than a single ingredient. Each element contributes to how the uncured liquid flows and how the cured part behaves.
Base polymer and additives
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Silicone polymer base
The backbone that gives the elastomer its flexibility and thermal stability.
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Reinforcing fillers
Added to build strength and tear resistance and to tune hardness and flow.
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Catalysts
Platinum-based systems that control how and how quickly the material cures.
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Pigments and other additives
Used for color matching, transparency targets and specific functional requirements.
Two-component supply
LSR is usually supplied as two components that stay separate until the moment of processing. They are combined in a metering and mixing unit and then injected. Because the cure begins once the parts are mixed, the material must be handled within its working window, and the processing equipment must keep the ratio consistent shot after shot.
Formulation changes the outcome
Formulation and additives affect color, hardness, cure time and application suitability. Two compounds with the same nominal hardness can still differ in flow, cure behavior and final properties, so the grade should be selected for the application, not just the number on the datasheet.
Key Properties of Liquid Silicone Rubber
LSR is valued for a combination of properties rather than any single one. The cards below summarize the main areas, and the notes that follow cover the conditions that shape them.
Flexibility and elasticity
LSR stays soft and elastic across a broad hardness range, from 10 to 80 Shore A in our standard capability, so designers can choose a compliant seal or a firmer grip.
Tear strength and durability
Grades are formulated to resist tearing under repeated flexing, which supports long service in seals and boots that are cycled daily.
Temperature stability
Silicone keeps useful flexibility over a wide temperature span. Exact limits depend on the grade and must be confirmed from supplier data.
Electrical and detail performance
LSR provides electrical insulation, low compression set, transparency options and the ability to reproduce fine molded details.
Weathering, chemicals and environment
Cured LSR resists weathering, UV exposure, ozone and moisture, and it tolerates many chemicals. Resistance is not universal, however. Fuels, oils, solvents and specific cleaning agents can affect different grades in different ways, which is why fluorosilicone and other specialty compounds exist for demanding chemical exposure.
Engineering note
Property values vary by formulation, grade and processing conditions, including cure temperature, post-cure and mold design. Treat any published figure as a starting point and verify it on your own part under real conditions.
How Is Liquid Silicone Rubber Manufactured and Molded?
Most LSR parts are produced by liquid silicone rubber injection molding. The process is straightforward in concept but depends heavily on control of ratio, temperature, timing and mold design.
The molding sequence
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1
Meter and mix
The A and B components are dosed at a controlled ratio and blended in a static or dynamic mixer.
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2
Inject into the mold
The mixed liquid is injected into a heated, closed mold cavity that defines the part geometry.
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3
Cure
Heat activates the platinum catalyst and the material crosslinks into a solid elastomer.
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4
Demold and inspect
The part is removed, checked for fill and flash, and passed to any secondary operations required.
Why platinum curing produces a stable elastomer
Platinum-catalyzed addition cure creates crosslinks without releasing volatile by-products during the reaction. Because nothing needs to escape from the part, the cured network is stable and the molded geometry is retained with minimal distortion. This is one reason platinum-cured LSR is widely used for parts that must remain dimensionally consistent over long production runs.
LSR injection molding is well suited to high-volume production and to complex geometries. Automated feeding and shot control make cycles repeatable, and the low-viscosity liquid can fill thin walls, undercut-free details and small sealing lips that would be hard to form in solid rubber.
Typical process capability
The figures below reflect the LSR injection molding capability at LSRParts. Actual results depend on geometry, material and tooling.
| Parameter | LSRParts capability |
|---|---|
| Maximum part envelope | 300 × 200 × 100 mm |
| Silicone hardness | 10–80 Shore A |
| Typical part tolerance | ±0.05 mm; critical features down to ±0.02 mm, application dependent |
| Mold manufacturing tolerance | ±0.01 mm |
| Part-to-part repeatability | Approx. ±0.1 mm, geometry dependent |
| Cavity configuration | Single-cavity or multi-cavity |
| Production mold life | 3–5 million shots, tooling and application dependent |
Secondary operations
Many parts need more than molding. Common follow-on steps include:
Post-curing to drive off residual volatiles and stabilize properties.
Trimming to remove flash and gate residue.
Bonding and overmolding onto plastic or metal substrates.
Printing, laser marking, drilling and assembly as required by the drawing.
What Are the Advantages of Liquid Silicone Rubber?
From a production standpoint, LSR offers three things that matter most to OEM programs: design freedom, consistent quality and suitability for automation.
Design flexibility
Fine features, thin walls and integrated sealing lips can be molded in one shot.
Consistent part quality
Metered mixing and controlled injection keep dimensions and properties stable across large batches.
Automated production
The process lends itself to automated molding cells, which supports repeat orders and predictable output.
Durability and long service life
In demanding environments such as outdoor seals, engine-bay connectors and repeatedly flexed boots, the combination of weather resistance, elasticity and low compression set supports long service life. The right grade and a sound seal design are what turn those properties into field performance.
Specialty grades
Biocompatible, food-contact or electrical grades may be available when a material is specifically formulated and tested for those uses. Never assume a general-purpose compound meets these requirements.
What Are the Downsides of Silicone Rubber?
LSR is not the right choice for every part. Being honest about its limits early avoids costly redesigns later.
Material and tooling cost
Compounds and precision molds usually cost more upfront than commodity rubbers.
Specialized equipment
Metering, mixing and injection units designed for two-component liquid silicone are required.
Precise mold design
Gate location, venting, parting lines and draft must be planned carefully to avoid flash and voids.
Grade-specific limits
Not every LSR grade resists every chemical, abrasion or tear condition equally well.
Bonding, finishing and recycling also need planning. Silicone does not bond readily to many materials, so adhesion strategy must be defined early. Surface finishing options are set by the mold texture and secondary steps. Recycling pathways for cured silicone are limited, as explained in the FAQ below.
Our recommendation
Evaluate total part cost and performance, not material price alone. A slightly more expensive grade that seals reliably for years, avoids rework and runs on a stable mold can cost far less per part than a cheaper compound that drifts out of tolerance.
What Is Liquid Silicone Rubber Used For?
LSR appears across industries wherever flexibility, sealing, insulation or environmental resistance is required. The sections below group the most common uses.
Application 01
Medical and healthcare
Seals, tubing, masks, wearable components and selected device parts. Medical programs typically call for regulated, traceable grades and documented validation.
Application 02
Automotive and electric vehicles
Gaskets, connector and wire seals, battery seals, sensor seals and protective components exposed to heat, weather or fluids.
Application 03
Electronics and electrical equipment
Keypads, insulators, waterproof housing seals and overmolded protective components.
Application 04
Consumer goods and food-related products
Kitchenware, wearable products, baby-care items and reusable components, where the grade meets the applicable requirements for that use.
Application 05
Industrial applications
Valves, diaphragms, grommets, seals and parts that need flexibility and resistance to the operating environment.
Is Liquid Silicone Rubber Safe?
Safety is not a property of the material name alone. It depends on the specific formulation, how the part is cured, its intended use and the regulatory requirements that apply to that use.
General-purpose LSR
Suitable for many industrial and electronics parts. It is not automatically suitable for skin contact, food contact or implantable use.
Tested or certified grades
Medical, food-contact and other regulated grades are supplied with documentation for their intended use and should be selected deliberately.
Verification step
Check supplier documentation for the specific grade, and run finished-part testing under the intended conditions of use. Documentation for a material does not automatically certify the finished part.
What Does Liquid Silicone Not Stick To?
Cured silicone has low surface energy, which is the reason it resists wetting and adhesion. Many common adhesives will not form a durable bond to it without preparation, and the same low energy that makes silicone release well from a mold makes bonding harder.
What affects adhesion
Silicone grade and whether it is a selective-adhesion formulation.
Substrate material, whether plastic or metal.
Surface condition, including cleanliness and any preparation before bonding.
Primers or bonding agents used in the process.
When chemical bonding is not practical, mechanical design features can hold the part in place. Undercuts, interlocking geometry, through-holes and retention rims give the silicone something to grip. Selective-adhesion grades and bonding strategies can also be considered during DFM review, depending on the substrate and production volume.
How to Choose the Right LSR Grade
Grade selection is most efficient when the requirements are written down before material discussions begin. Work through the list below with your engineering and quality teams.
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1
Operating temperature
Define the continuous and peak temperatures the part will see in service.
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2
Chemical exposure
List fluids, fuels, cleaners and oils the part contacts, including intermittent exposure.
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3
Hardness and mechanical needs
Specify the Shore A hardness range, tear and compression requirements, and any flex-cycle demands.
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4
Color and transparency
Decide whether the part needs a matched color, a specific surface texture or an optical-clear appearance.
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5
Regulatory requirements
Identify any medical, food-contact or electrical requirements and the documentation they demand.
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6
Volume, mold design and compatibility
Confirm expected annual volume, the mold strategy and any substrates the silicone must join with.
Common LSR material families
The families below are offered at LSRParts. Final selection should always be confirmed against the specific application and documentation.
| Material family | Typical target applications |
|---|---|
| General purpose LSR | Industrial, electronics |
| Medical grade LSR | Medical devices |
| Food grade LSR | Food, beverage, baby care |
| Platinum-cured silicone | Medical, food contact |
| Optical LSR | Optical, lighting |
| Fluorosilicone | Automotive, fuel and chemical exposure |
| High-temperature silicone | Automotive, industrial |
| Low-temperature silicone | Outdoor, automotive |
| Electrically conductive silicone | Electronics, EMI |
| Thermally conductive silicone | Thermal management |
| Flame-retardant silicone | Electrical, automotive |
| Custom compounds | Application-specific requirements |
Test before you commit
Build prototypes and test them under real-world conditions, including temperature cycling, chemical exposure and assembly forces, before committing to production tooling. Early sampling is far cheaper than changing a production mold.
Frequently Asked Questions About Liquid Silicone Rubber
Is liquid silicone the same as rubber?
After curing, LSR becomes an elastic, rubber-like material that behaves like rubber in use. It is not natural rubber, though, because its chemistry is based on a silicone polymer rather than a natural polyisoprene.
What are the main disadvantages of silicone rubber?
The main considerations are higher material and tooling cost, the need for specialized processing equipment and precise mold design, bonding challenges with many substrates, and performance limits that differ from grade to grade.
Is liquid silicone rubber safe for skin or food contact?
Only appropriately formulated and tested grades should be used for these applications. Confirm the grade's documentation for the intended use and validate the finished part under real conditions of use.
Can liquid silicone rubber be recycled?
Recycling options depend on the material, the product design and the processing infrastructure available. Cured silicone is not typically remelted like thermoplastic plastic, so end-of-life planning should be considered during design.
Next step
Talk to our engineers about your LSR part
LSRParts is a precision silicone components manufacturer focused on custom liquid silicone rubber molding and production-ready parts. We support OEMs and product teams from early DFM review and material selection through mold design, sampling, validation and mass production. If you have drawings or 3D files and need a grade recommendation, send us your requirements and we will review them with you.
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